High voltage installations in high voltage power transmission systems comprise apparatus that are located dose to or in galvanic contact with the high voltage circuit. Examples of such apparatus are switching elements, series capacitors, sensors for voltage and current, and monitoring and protective equipment.
Such apparatus require auxiliary power for their operation and various methods and means for supply thereof exist in the state of the art.
According to one known principle, the auxiliary power is tapped off from the high voltage circuit, for example by the use of voltage or current transformers. The method thus requires that the high voltage circuit is energized and, to ensure proper operation of the apparatus in question, that after the energization, it has settled to such an extent that the auxiliary power can be safely used. However, the energization process is often a critical event in the operation of the high voltage circuit, and consequently, an auxiliary power supply that is independent of the state of the high voltage circuit is highly desirable.
According to another known principle, the auxiliary power is generated at ground voltage potential and transmitted to the high voltage circuit. In the high voltage installations in question, such auxiliary power is usually available at ground level as a direct voltage supply, for example at 110 DC, supported by a battery backup.
A basic problem is then to provide insulation between the ground voltage potential and the high voltage potential of the high voltage installation. Means for providing such insulation have to satisfy the requirements set by international norms and standards.
One known method, used in particular for switching elements such as circuit breakers and disconnectors, is to create a mechanical movement at ground potential and transmit this movement to high potential using insulating rods, which rods thus provide the necessary insulation between the two different potentials. The method requires a driving mechanism at ground potential and rod and link system at high potential that makes the equipment mechanically complex and results in unavoidable delays in the operating times.
Another known method, used in particular in connection with current and voltage sensors, is to convert the auxiliary power at ground potential to optical power, transmit the power to high potential via an optical link, and then convert the optical power back to electric power. With this method only very small amounts of power, typically in the order of fractions of watts, can be transmitted.
Thus, there is a need for an auxiliary power supply equipment wherein the power is generated at ground level to make it independent of the state of the high voltage circuit, and which equipment can handle amounts of power sufficient for the operation of high power apparatus such as switching element and series capacitor installations.